Various types of color display units using liquid crystals have been presented. Among them are color liquid crystal display units which form a color filter layer using the inside surface of a liquid crystal cell. The characteristics of red, green and blue micropatterns are such that the cell structure is relatively simple and full color display is possible.
This invention relates to improvements of color liquid crystal display units which have red, green and blue micropatterns and enable full color display.
A former color liquid display unit Da is, as shown in FIG. 21, composed of a relief pattern comprising gelatin, glue or casein combining color filters 6-9a, 6-10a, and 6-11a dyed to red, green and blue, a twisted nematic liquid crystal layer 6-36a, and two photolithography type neutral polarizers 6-37a and 6-37b.
Another former color liquid crystal display unit Dc is, as shown in FIG. 22, composed by combining color polarizers 6-9c, 6-10c, and 6-11c in which dichromatic dyes are lined up in one direction, with a neutral polarizer 6-37c (see patent publication gazette No. SHO 58-7177 and 58-17420).
In the color liquid crystal display unit Da, usually two neutral polarizers 6-37a and 6-37b are positioned so that their directions of polarization (arrow Fa and Fb) are parallel, black is displayed when no voltage is applied to the transparent electrodes 6-24a, 6-18a, 6-19a, and 6-20a, and when voltage is applied, liquid crystal molecules rise in the direction of the electric field to display the colors of the color filters themselves. Therefore, by selecting the voltage to be applied to each picture element of red, green and blue independently and freely, the desired colors can be displayed on the black base.
However, there was a problem in this type of color liquid crystal display unit Da in that only one-third of the picture elements can contribute to the display in case of single-color display of red, green or blue and the remainder of the display is dark.
In order to solve this problem, a light source may be placed on the back side of the display to achieve a higher contrast and brighter display. This is undesirable, however, since the primary advantages of liquid crystal display units are low power consumption and thinness. These advantages are reduced if a light source is to be arranged on the back side.
The problem with color liquid crystal display unit Dc is that only one-third of the picture elements can contribute to the display in the case of single-color display of red, green or blue, as in the above color liquid crystal display unit Da. In addition, a total display of black is impossible. When there is no electric field, the direction of polarization of the linear polarization agrees with the absorption axis direction of the color polarizers 6-9c, 6-10c, and 6-11c and they are seen as red, green and blue colors. When an electric field is applied, the linear polarization is not absorbed by the color polarizers 6-9c, 6-10c, or 6-11c, and they are seen as colorless. In the color liquid crystal unit Dc, colors are displayed in white or no color and therefore the entire display is brighter but, on the other hand, the display contrast is inferior.